The use of air treatment units in home, commercial and institutional facilities has been well accepted. These units (hereinafter collectively referred to as HVAC) typically provide heating, ventilation, dehumidification and/or air conditioning to a facility. Some examples of these air treatment units include, in particular, wall mounted HVAC units. Wall mount air treatment units include all of the necessary functional elements to condition and circulate air, and typically include circulating fans, a compressor, air cooling and heating heat exchangers, and filters. These elements of the unit are all typically mounted within or associated with a common housing provided with air intakes and exhausts as well as air supply and air return openings or ducts. The housing is mounted to a wall of a building, which is provided with spaced openings corresponding to the air supply and air return openings of the unit whereby conditioned air may be supplied to one or more rooms of the building via the supply opening and removed therefrom via the return opening.
When HVAC units are attached directly to a building wall and connected to one or more rooms by openings formed through room walls and/or ductwork, a relatively new structure by which air treatment units may be attached to the building to be supplied with conditioned air is referred to as a curb. At the present time, curbs function largely as a convenient means by which different sized air treatment units may be adapted to a pre-existing opening in a building.
One common application for wall mount units includes the heating, cooling and ventilation of school facilities and classrooms. Until recently, maximum allowable sound levels for these types of units have been largely unregulated. However, in the late 1990s the Los Angeles Unified School District (LAUSD) issued specifications permitting a maximum of 50 dbA background sound levels in classrooms. Manufacturers of air treatment units have been compelled to contemplate significant and expensive redesign of HVAC units in order to contribute less air treatment noise to the overall sound levels. Recently, some specifications have required a maximum of 45 dbA and, more recently, the American National Standards Institute (ANSI) passed a sound standard for schools requiring a maximum sound level of 35 dbA. The Acoustical Society of America, for example, and others are now attempting to get this latest, more stringent limit written into specifications.
The 35 dbA specification may prove to be a difficult standard to meet, and in some instances may prove to be impossible without a major redesign of existing units and, of course, the costs will ultimately be passed on to consumers (and to taxpayers). Accordingly, there is a demand for wall mount HVAC units that generate and contribute to the schoolroom or any room environment a minimal amount of noise, and which preferably is accomplished without a major and expensive redesign of existing products. The present invention greatly reduces sound levels and thus satisfies the demand.